<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <input type="text" v-model="username">
    </div>
    <script src="./lib/vue-2.6.12.js"></script>
    <script src="./lib/jquery-v3.6.0.js"></script>
    <script>
        const vm = new Vue({
            el: '#app',
            data: {
                username: 'admin'
            },
            //所有的 侦听器, 都应该被定义到 watch节点下

            watch: {
                //定义对象格式的侦听器
                username: {
                    //侦听器的处理函数
                    handler(newVal, oldVal) {
                        console.log(newVal, oldVal);
                    },
                    //immediate 选项的默认值是false
                    //immediate 的作用 : 控制侦听器是否自动触发一次
                    immediate: true
                }
            }
        })
    </script>
</body>

</html>